1. Field of the Invention
The present invention relates to a data distribution method and a data distribution apparatus for distributing various different types of data items through a plurality of communication lines or networks such as satellite lines, ground wire lines, and the like.
2. Description of the Related Art
FIG. 25 is a diagram showing the configuration of a conventional data distribution apparatus that has been disclosed in Japanese laid-open publication number JP-A-7/143181. This conventional data distribution apparatus comprising a connection device 103 in a transmitter and a connection device in a receiver for selecting one of a digital communication satellite 101 and a digital ground line 102 according to predetermined conditions such as the amount of transmission data to be transmitted, connection types such as a broadcast communication and a one to one point communication, and a traffic of a line. The connection devices 103 and 104 in the transmitter and the receiver are used as network connection apparatus placed between a digital communication satellite as a digital transmission path to connect private networks and a digital ground network, and the private networks.
The connection device 103 (a central station GW) in the transmitter is connected to the private network 106 (a central station LAN) that is connected to a large-volume information storage source 105 such as a digital video server 105 and the like. On the other hand, each of the connection devices 104 in a receiver (branch GW) is connected to a video terminal 108 through each branch private network 107. A video information broadcasting is performed from the connection device 103 in a transmitter to the connection device 104 in a receiver. In addition, a digital ground line or network connects the connection device in the transmitter 103 to the connection device 104 in a receiver. It is thereby possible to transmit control information and the like between them in two-way transmission.
FIG. 26 is a diagram showing a conventional process flow of a general transmission confirmation pattern. In the conventional transmission confirmation pattern, the transmission confirmation is performed on every receiving of a distribution data item. That is, the number of the distribution data items is equal to the number of the transmission confirmations. The timing to transfer the transmission confirmation is a time when the distribution data item is received.
FIG. 27 is a diagram showing a concept of a general configuration of a data communication system and a data process flow in which a receiver receives a data item and transmits a transmission confirmation to a transmitter (not shown). In the conventional data distribution system shown in FIG. 27, the control device 110 in a receiver receives a distribution data item through the satellite line 113 and then transfers this data item to the receive device 112 connected through the LAN 111. The receive device 112 transmits the transmission confirmation to the transmitter (not shown).
There are following prior art techniques (1) to (11) (relating to the above data distribution technique).
(1) Japanese laid-open publication number JP-A-62/189823 shows a technique in which a ground line and a satellite line are switched according to the state of those lines, and the configuration and the length of transmission data. This technique uses a two-way satellite line. There is therefore a drawback in that it is nessary to place a satellite receiver having a highly installation cost at every required point.
(2) Japanese laid-open publication number JP-A-2/16847 shows a method to designate a requirement of a transmission confirmation when a receiver requests a data transmission to a transmitter. However, this technique is limited only to a PULL type data distribution in which the request transmitted from the receiver becomes a trigger. That is, this technique cannot be applied to a PUSH type data distribution caused by the transmitter. There is therefore a drawback that it is difficult to designate a transmission confirmation in the PUSH type data distribution.
(3) Japanese laid-open publication number JP-A-4/367135 shows a technique in which the load required for the processing of affirmation response is reduced by grouping a plurality of affirmation requests into one frame and transmitting it. However, there is a drawback that it takes many clock times to make the frame and to analyze the frame when the number of the affirmation requests is small and when a plurality of affirmation requests do not happened simultaneously. In addition to this drawback, there is a drawback in that processing must wait until a plurality of affirmation requests are generated in order to group them into one frame. Therefore this technique can not be applied to a data distribution to be executed at a high speed.
(4) Japanese laid-open publication number JP-A-4/207430 shows a method in which a transmitter divides a file into a plurality of sub-files and the transmission confirmation is performed only when the all sub-files have been transmitted to a receiver. This means that a transmission affirmation is performed after all of the original file (not every a divided sub-file) to be distributed in the transmitter is recieved. Therefore there is a drawback that the load of the transmitter becomes large when the number of distribution files or the number of receivers is increased, because the number of-transmission affirmations received by the transmitter becomes a value of (the number of transmitted files).times.(the number of receivers).
(5) Japanese laid-open publication number JP-A-63/276928 shows a time division transmission point reservation method in which a shared transmission path is used as a transmission confirmation process during a desired time period. Because this conventional technique exclusively uses the transmission path during the desired time period, there is a drawback that it is difficult to use the transmission path for urgent transmission during this time period
(6) Japanese laid-open publication number JP-A-60/24749 shows a transmission confirmation method in which a transmission confirmation transferred from a relay node is canceled and, only a transmission confirmation and a re-transmission request transmitted from a receiver are accepted by a transmitter in a data communication system having relay nodes. This causes an increase load on the relay node because the relay node performs a transmission confirmation operation having no meaning.
(7) Japanese laid-open publication number JP-A-62/299142 shows a transmission confirmation method in which a control host in a receiver performs a transmission confirmation without waiting to receive a transmission confirmation transferred from the host in the receiver. Therefore there is a drawback that there is no consideration when the host in the receiver fails to receive the data. In addition to this drawback, there is no control meaning in transmitting the transmission confirmation data item from the host in the receiver to the receiver control host.
(8) Japanese laid-open publication number JP-A-62/189823 further shows a line combination communication method in which a target line to be used is selected according to a configuration of data, a size, a traffic state of a line and the like. However, it is not decided how to set and to use a threshold value of a data size when a current channel is switched in this method. Further, this method has a drawback that a distribution packet number per time is fixed and only a static time T="td".times."tx" is considered, where "td" is a time required for switching, and "tx" is a satellite delay time. Although the state of data communication using satellite lines is influenced by weather conditions, this method has a drawback in which there is no consideration for un-reached packet and transmission delay.
(9) Japanese laid-open publication number JP-A-62/285529 shows a satellite communication method of distributing small sized data through ground lines and of transmitting large volume data by satellite lines after data is divided into two groups such as the small sized data group and the large sized data group. However, this method involves a drawback in which it is not considered to transmit a plurality of small sized data items such as "WWW" data in parallel, because a general data item must be a large sized volume and a control data item must be a small sized data item in this method.
(10) Japanese laid-open publication number JP-A-3/195234 shows a packet exchange method in which a most suitable ground line is selected and used when a current satellite line has a malfunction. This method involves a drawback in which traffic on the ground line to transfer data becomes heavy when the number of un-completed transmission packets is increased, because the packet data item with regard to the un-completed transmission packet is returned to a control device in a transmitter.
(11) Japanese laid-open publication number JP-A-3/195234 shows a method in which the number of distribution data items that were not distributed correctly is counted, and a data transmission time to a receiver is controlled according to this counted number. However, this method involves a drawback in which a load of a network is increased because a re-transmission operation is executed on every occurrence of a packet transmission failure.
Because the conventional data distribution apparatus and methods have the configuration described above, following drawbacks (12) to (20) are caused:
(12) In general, although the most suitable transmission confirmation pattern is changed according to a change in distribution conditions such as the number of receivers, a receive data buffer size of the receiver and the like, there is no method to solve the above problems.
(13) Although the most suitable transmission confirmation pattern is also changed in the same receiver according to a change of the distribution conditions described above, there is no technique to match the change of the distribution conditions.
(14) Furthermore, the transmission confirmation pattern described above is transmitted every transmission in one-to-one correspondence. That is, when the data transmission distribution is performed two times, the transmission confirmation is also transferred two times. Accordingly, many data transmissions must be performed, the receiver must transfer the transmission confirmations whose number is equal to the number of distribution files in the data transmissions. This causes an increase in the load of receiver.
(15) Moreover, when a transmission station broadcasts data to receivers, the transmission station must receive the transmission confirmations, whose number is equal to the number of the receivers, transmitted from the receivers, simultaneously. In this case, when the number of the receivers is increased, the number of the transmission confirmations to be received simultaneously is also increased. This causes an increase in the load of the transmission station.
(16) Further, in a case that a receive station comprises a receive control device and receivers connected to the receive control device through a Local Area Network (LAN), the receiver generates a transmission confirmation and sends it to a transmitter and it is difficult to change the above receivers function. Therefore there is a drawback that the receiver performs the transmission confirmation operation even if the load of the receiver is heavy.
(17) In addition, there is a drawback that the use of a satellite line for the transmission of a small-sized data becomes uneconomical in performance and maintenance cost. Because the technique, disclosed in the Japanese laid-open publication number JP-A-7/143181 that has been prescribed, uses a N-ISDN line as a wire line, the maintenance cost or the operating costs of them becomes very high.
(18) Furthermore, there is a drawback in which a transmission distribution is executed again after a line is restored to normal conditions when the line is down by a failure of a relay device and the like.
(19) Moreover, there is no advantage to use a satellite line and a ground line that are capable of transmitting data with a high speed when a plurality of small sized data items are transmitted simultaneously.
(20) Finally, when a packet transmission has failed, a re-transmission for this failed packet must be executed by interrupting the current packet transmission. Therefore there is a drawback in which the transmission efficiency of a transmitter becomes low because a transmission for a current packet must be interrupted during a required time period in order to perform the re-transmission for the failed packet. Then the current packet transmission will be re-started after every occurrence of a packet failure.